The coordinated regulation of gene expression is a fundamental process in biology. In this proposal, we explore the role of poly (ADP-ribose) polymerase-1 (PARP-1) and its associated factors in the chromatin- dependent control of transcription in response to cellular signaling by a steroid hormone, estrogen, and a cytokine, tumor necrosis factor alpha (TNF?). PARP-1 is an abundant, chromatin-associated enzyme that catalyzes the polymerization of poly (ADP-ribose) (PAR) chains on target proteins from donor nicotinamide adenine dinucleotide (NAD+) molecules. PARP-1 plays key roles in a variety of physiological and pathological systems, including hormonal signaling, metabolism, inflammation, differentiation, adipogenesis, carcinogenesis, development, and aging. The long-term objective of these studies is to achieve a better understanding of the chromatin-dependent molecular mechanisms underlying signal-regulated transcription by PARP-1 and its associated factors. Our broad hypothesis is that the gene regulatory activities of PARP-1 are determined by: (1) the local chromatin environment (e.g., chromatin composition, histone modifications), (2) physical and functional interactions among PARP-1, transcription factors (e.g., ER?, NF-?B), histone-modifying coregulators, and components of chromatin, (3) the targets of PARP-1 enzymatic activity, and (4) the availability of NAD+ in the nucleus. We will test this hypothesis as it relates to estrogen- and TNF?-dependent gene regulation by using an integrated approach that combines a complementary set of tools from biochemistry, molecular biology, cell biology, chemical biology, and genomics. Specifically, we will determine (1) the chromatin-dependent molecular mechanisms of PARP-1 localization and activity at target gene promoters, including the role of the histone variants H2A.Z and H3.3; (2) the effects of PARP-1-dependent site- specific PARylation on the activity and function of chromatin-regulating proteins, including the histone demethylase KDM5B and the histone methyltransferase Ezh2; and (3) the mechanisms by which NAD+ production by the nuclear NAD+ synthase nicotinamide mononucleotide adenylyltransferase-1 (NMNAT-1) regulates PARP-1 enzymatic activity at target gene promoters. Collectively, these studies will provide new insights into the molecular mechanisms of PARP-1's gene regulatory activities in the context of chromatin, especially in relation to estrogen and TNF? signaling, and nuclear NAD+ biosynthesis and availability. Given the important role of PARP-1 in human disease, as well as its potential drugability, our studies could lead to new ways to exploit these factors as therapeutic targets.